Yes, incredible though it may seem, that door and narrow little window in the brick wall between the two clad and painted houses, is actually the frontage of a third house, officially recognised as the narrowest occupied domestic residence in Britain.
It is in Manor Road, in Fratton (or Buckland, as my mother always insisted on calling it) and was built by my grandfather Edgar Bedford, sometime in the early part of the 20th century, when a local businessman spotted an opportunity.
(* There's a small anomaly in all this, in that records on Manor Road I have studied lately suggest that this house was built in 1899; my grandfather would have been in his early twenties then and he had started an independent building business as soon as he finished his apprenticeship, so it still works, chronologically.
It's also possible that the original records could be a few years adrift, as they were often compiled retrospectively, so 1899 could well have been 1909, or any year in between.
On the other hand, this entire story may have been apocryphal anyway! Not to worry, though - 'cos Portsmouth still has the narrowest house, either way! )
Originally, the houses in Manor Road had been built from either end, working towards a spot about a third of the way up from where the road joined Fratton Road and there was a small, wedge-shaped piece of land left in the middle, which stood vacant for many years.
The businessman - my mother always told me his name was Barney Shine, but that's only anecdotal evidence at best - asked my grandfather if he could fit a house into the plot.
"If I can fit a door into the front," my grandfather is supposed to have replied, "then I can fit a b***** house into it." And that's precisely what happened. The house is 4 feet ten inches wide at the pavement and the little plaque below the bedroom window confirms its status as the narrowest house in the country.
The building widens out as it goes back and that feature can produce a strange foreshortening effect when you're inside, but over the years, it has been home to many families, including, in the 1970s, a young lady who worked for me, who bought it with her husband, shortly after they were married.